Pyelonephritis continues to result in considerable morbidity, mortality and health care expense. In order to develop new treatment strategies as well as understand who is at risk for pyelonephritis, a better understanding of the kidney's role i the innate defense of the kidney and urinary tract is needed. Our research has identified a murine model of intercalated cell deficiency that is susceptible to pyelonephritis. We have also demonstrated that in mice and humans intercalated cells are involved in production and secretion of antimicrobial peptides. Others have demonstrated that intercalated cells act as the first site in the kidney that responds to Gram-negative organisms via Toll-like 4 receptor (TLR4) signaling pathways. Thus, surmounting evidence suggests that intercalated cells play a critical role in the innate defense of the kidney. We hypothesize that key kidney acid-base mediators are required for renal innate immune function. To build on our previous studies, we have devised three specific aims that will thematically examine the role of intercalated cells in innate defense of the kidney. In Specific Aim 1, we will correlate human antimicrobial production with carbonic anhydrase inhibition to our carbonic anhydrase murine models. Next, we will dissect the role of renal carbonic anhydrase in our mouse model of congenital intercalate cell deficiency by performing kidney transplants. In Specific Aim 2, the antimicrobial response that is TLR4 dependent and independent will be elucidated using an intercalated cell-specific TLR4 conditional knockout approach. Finally, in Aim 3, we have developed a murine model acquired loss of intercalated cells using a diphtheria toxin murine model. These Aims, while interconnected, will adequately and independently test the hypothesis presented in this application. Our long-term research goal is to develop new pyelonephritis treatment strategies that reduce antibiotic exposure and preserve renal function in populations at risk. The proposed research will provide the foundation to include modulation of acid-base mediators in pyelonephritis management, thereby expanding treatment scope beyond antibiotics.